Unrolled-collections

Unrolled collections

PowerShell may unroll collections, that is replace an original collection with an array of its items or just a single item.

This fact is especially easy to forget for some complex objects like [System.Data.DataTable]. PowerShell may treat it as a collection of [System.Data.DataRow] and the original table instance may be "lost".

The common workaround is use of the comma operator which wraps an argument with an array of a single item. This array is unrolled and this gets its single item as it is, not unrolled.

Scripts

• Test-1-unrolled-adding.ps1 shows unrolling on adding items to an array using +=.
• Test-2-unrolled-output.ps1 shows a collection unrolled on output from a function.
• Test-3-unrolled-return.ps1 is the similar script which uses return explicitly.
• Test-4-unrolled-if.ps1 shows how if ($x) {$y} unrolls data, see also Missing-ternary-operator.

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• Stack Overflow Append an Array to an Array of Arrays
• Stack Overflow Strange behaviour in function returning DataSet/DataTable
• PowerShellTraps/issues/5